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kbuild: avoid too many execution of scripts/pahole-flags.sh

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scripts/pahole-flags.sh is executed so many times.

You can confirm it, as follows:

  $ cat <<EOF >> scripts/pahole-flags.sh
  > echo "scripts/pahole-flags.sh was executed" >&2
  > EOF

  $ make -s
  scripts/pahole-flags.sh was executed
  scripts/pahole-flags.sh was executed
  scripts/pahole-flags.sh was executed
  scripts/pahole-flags.sh was executed
  scripts/pahole-flags.sh was executed
    [ lots of repeated lines... ]

This scripts is executed more than 20 times during the kernel build
because PAHOLE_FLAGS is a recursively expanded variable and exported
to sub-processes.

With GNU Make >= 4.4, it is executed more than 60 times because
exported variables are also passed to other $(shell ) invocations.
Without careful coding, it is known to cause an exponential fork
explosion. [1]

The use of $(shell ) in an exported recursive variable is likely wrong
because $(shell ) is always evaluated due to the 'export' keyword, and
the evaluation can occur multiple times by the nature of recursive
variables.

Convert the shell script to a Makefile, which is included only when
CONFIG_DEBUG_INFO_BTF=y.

[1]: https://savannah.gnu.org/bugs/index.php?64746

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Alan Maguire <alan.maguire@oracle.com>
Tested-by: Alan Maguire <alan.maguire@oracle.com>
Reviewed-by: Nicolas Schier <n.schier@avm.de>
Tested-by: Miguel Ojeda <ojeda@kernel.org>
Acked-by: Miguel Ojeda <ojeda@kernel.org>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
This commit is contained in:
Masahiro Yamada
2023-10-19 00:19:48 +09:00
parent 7f6d8f7e43
commit 72d091846d
4 changed files with 21 additions and 34 deletions
Download Patch File Download Diff File Expand all files Collapse all files

19
scripts/Makefile.btf Normal file
View File

@@ -0,0 +1,19 @@
# SPDX-License-Identifier: GPL-2.0
pahole-ver := $(CONFIG_PAHOLE_VERSION)
pahole-flags-y :=
# pahole 1.18 through 1.21 can't handle zero-sized per-CPU vars
ifeq ($(call test-le, $(pahole-ver), 121),y)
pahole-flags-$(call test-ge, $(pahole-ver), 118) += --skip_encoding_btf_vars
endif
pahole-flags-$(call test-ge, $(pahole-ver), 121) += --btf_gen_floats
pahole-flags-$(call test-ge, $(pahole-ver), 122) += -j
pahole-flags-$(CONFIG_PAHOLE_HAS_LANG_EXCLUDE) += --lang_exclude=rust
pahole-flags-$(call test-ge, $(pahole-ver), 125) += --skip_encoding_btf_inconsistent_proto --btf_gen_optimized
export PAHOLE_FLAGS := $(pahole-flags-y)

30
scripts/pahole-flags.sh
View File

@@ -1,30 +0,0 @@
#!/bin/sh
# SPDX-License-Identifier: GPL-2.0
extra_paholeopt=
if ! [ -x "$(command -v ${PAHOLE})" ]; then
exit 0
fi
pahole_ver=$($(dirname $0)/pahole-version.sh ${PAHOLE})
if [ "${pahole_ver}" -ge "118" ] && [ "${pahole_ver}" -le "121" ]; then
# pahole 1.18 through 1.21 can't handle zero-sized per-CPU vars
extra_paholeopt="${extra_paholeopt} --skip_encoding_btf_vars"
fi
if [ "${pahole_ver}" -ge "121" ]; then
extra_paholeopt="${extra_paholeopt} --btf_gen_floats"
fi
if [ "${pahole_ver}" -ge "122" ]; then
extra_paholeopt="${extra_paholeopt} -j"
fi
if [ "${pahole_ver}" -ge "124" ]; then
# see PAHOLE_HAS_LANG_EXCLUDE
extra_paholeopt="${extra_paholeopt} --lang_exclude=rust"
fi
if [ "${pahole_ver}" -ge "125" ]; then
extra_paholeopt="${extra_paholeopt} --skip_encoding_btf_inconsistent_proto --btf_gen_optimized"
fi
echo ${extra_paholeopt}